Rate Matters - West Companies (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Oct. 26, 2017	Sep. 30, 2017	Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		$ 3,710.0	$ 3,183.9
Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		114.0	148.2
Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		145.2	$ 113.8
AEP Texas Interim Transmission and Distribution Rates [Member]
Public Utilities, General Disclosures [Line Items]
AEP Texas Cumulative Revenues Subject to Review		697.0
Hurricane Harvey Storm [Member]
Public Utilities, General Disclosures [Line Items]
Annual Recovery of Storm Costs through Base Rates		1.0
AEP Texas Total Storm-Related Costs		97.0
AEP Texas Hurricane Harvey Storm-Related Costs		$ 73.0
ETT Interim Transmission Rates [Member]
Public Utilities, General Disclosures [Line Items]
Parent Ownership Interest In ETT		50.00%
AEP Share Of ETT Cumulative Revenues Subject To Review		$ 709.0
FERC Transmission Complaint - AEP SPP Participants [Member]
Public Utilities, General Disclosures [Line Items]
Approved Return on Common Equity		10.70%
Intervenor Recommended Return on Common Equity		8.36%
2012 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
2013 Reversal of Previously Recorded Regulatory Disallowances		$ 114.0
Resulting Approved Base Rate Increase		52.0
2012 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
2013 Reversal of Previously Recorded Regulatory Disallowances		114.0
Resulting Approved Base Rate Increase		$ 52.0
2016 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Requested Return on Common Equity		10.00%
Recommended Investment Disallowance Resulting in Possible Write-Offs		$ 89.0
Requested Net Increase in Texas Annual Revenues		69.0
Amount Of Increase Related To Environmental Controls		34.0
Amount of Increase Related to Additonal Investment and Increased Operating Costs		25.0
Amount of Increase Related to Transmission Cost Recovery		8.0
Amount of Increase Related to Vegetation Management		$ 2.0
Texas Jurisdictional Share of the Welsh Plant		33.00%
Amount of Write-Off Related to Environmental Controls		$ 40.0
Amount of Write-Off Related to Welsh Plant Unit 2		25.0
ALJ Proposed Net Increase in Texas Annual Revenues		$ 50.0
ALJ Proposed Return on Equity		9.60%
ALJ’s Total Proposed Amount of Write-Off		$ 22.0
ALJ’s Proposed Amount of Write-Off Related to Welsh Plant Unit 2		$ 9.0
2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Return on Common Equity		10.00%
Recommended Investment Disallowance Resulting in Possible Write-Offs		$ 89.0
Requested Net Increase in Texas Annual Revenues		69.0
Amount Of Increase Related To Environmental Controls		34.0
Amount of Increase Related to Additonal Investment and Increased Operating Costs		25.0
Amount of Increase Related to Transmission Cost Recovery		8.0
Amount of Increase Related to Vegetation Management		$ 2.0
Texas Jurisdictional Share of the Welsh Plant		33.00%
Amount of Write-Off Related to Environmental Controls		$ 40.0
Amount of Write-Off Related to Welsh Plant Unit 2		25.0
ALJ Proposed Net Increase in Texas Annual Revenues		$ 50.0
ALJ Proposed Return on Equity		9.60%
ALJ’s Total Proposed Amount of Write-Off		$ 22.0
ALJ’s Proposed Amount of Write-Off Related to Welsh Plant Unit 2		$ 9.0
Louisiana Turk Plant Prudence Review [Member]
Public Utilities, General Disclosures [Line Items]
Louisiana Jurisdictional Share Of Turk Plant		33.00%
Louisiana Turk Plant Prudence Review [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Louisiana Jurisdictional Share Of Turk Plant		33.00%
Louisiana 2015 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		$ 14.0
Louisiana 2015 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		14.0
Louisiana 2017 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		31.0
Louisiana 2017 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		31.0
Oklahoma Base Rate Case - 2017 [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		$ 156.0
Requested Return on Common Equity		10.00%
Amount of Increase Related to Annual Depreciation Rates		$ 42.0
Recommended Disallowance for Capitalized Incentives		38.0
Recommended Potential Refund Related to an SPP Rider		43.0
Combined Potential Write-off and Refund		163.0
Oklahoma Base Rate Case - 2017 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		$ 156.0
Requested Return on Common Equity		10.00%
Amount of Increase Related to Annual Depreciation Rates		$ 42.0
Recommended Disallowance for Capitalized Incentives		38.0
Recommended Potential Refund Related to an SPP Rider		43.0
Combined Potential Write-off and Refund		163.0
Oklahoma Base Rate Case - 2017 [Member] | Northeastern Plant, Unit 4 [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		82.0
Oklahoma Base Rate Case - 2017 [Member] | Northeastern Plant, Unit 4 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		82.0
Oklahoma Base Rate Case - 2017 [Member] | Northeastern Plant, Unit 3 [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		346.0
Oklahoma Base Rate Case - 2017 [Member] | Northeastern Plant, Unit 3 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		346.0
Welsh Plant, Units 1 and 3 - Environmental Projects [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		850.0
Construction Work in Progress		398.0
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs		79.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals		11.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity		6.0
Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs		131.0
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		850.0
Construction Work in Progress		398.0
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs		79.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals		11.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity		6.0
Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs		131.0
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Welsh Plant, Units 1 and 3 [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		626.0
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Welsh Plant, Units 1 and 3 [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		$ 626.0
FERC SWEPCo Power Supply Agreements Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Approved Return on Common Equity		11.10%
Intervenor Recommended Return on Common Equity		8.41%
Minimum [Member] | 2016 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Return on Equity		9.20%
Recommended Net Increase in Texas Annual Revenues		$ 36.0
Minimum [Member] | 2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Return on Equity		9.20%
Recommended Net Increase in Texas Annual Revenues		$ 36.0
Minimum [Member] | Oklahoma Base Rate Case - 2017 [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Net Increase in Oklahoma Annual Revenues		$ 28.0
Recommended Return on Equity		8.00%
Minimum [Member] | Oklahoma Base Rate Case - 2017 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Net Increase in Oklahoma Annual Revenues		$ 28.0
Recommended Return on Equity		8.00%
Minimum [Member] | Oklahoma Base Rate Case - 2017 [Member] | Northeastern Plant, Unit 4 [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Investment Disallowance Resulting in Possible Write-Offs		$ 27.0
Minimum [Member] | Oklahoma Base Rate Case - 2017 [Member] | Northeastern Plant, Unit 4 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Investment Disallowance Resulting in Possible Write-Offs		$ 27.0
Maximum [Member] | 2016 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Return on Equity		9.35%
Recommended Net Increase in Texas Annual Revenues		$ 47.0
Maximum [Member] | 2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Return on Equity		9.35%
Recommended Net Increase in Texas Annual Revenues		$ 47.0
Maximum [Member] | Oklahoma Base Rate Case - 2017 [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Net Increase in Oklahoma Annual Revenues		$ 108.0
Recommended Return on Equity		9.00%
Maximum [Member] | Oklahoma Base Rate Case - 2017 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Net Increase in Oklahoma Annual Revenues		$ 108.0
Recommended Return on Equity		9.00%
Maximum [Member] | Oklahoma Base Rate Case - 2017 [Member] | Northeastern Plant, Unit 4 [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Investment Disallowance Resulting in Possible Write-Offs		$ 82.0
Maximum [Member] | Oklahoma Base Rate Case - 2017 [Member] | Northeastern Plant, Unit 4 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Investment Disallowance Resulting in Possible Write-Offs		$ 82.0
Subsequent Event [Member] | Louisiana Turk Plant Prudence Review [Member]
Public Utilities, General Disclosures [Line Items]
LPSC Staff Recommendation for Potential Disallowance Related to Turk Plant	$ 51.0
LPSC Staff Recommended Percentage Reduction of the Return on Common Equity for the Turk Plant	1.00%
Subsequent Event [Member] | Louisiana Turk Plant Prudence Review [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
LPSC Staff Recommendation for Potential Disallowance Related to Turk Plant	$ 51.0
LPSC Staff Recommended Percentage Reduction of the Return on Common Equity for the Turk Plant	1.00%
Subsequent Event [Member] | Minimum [Member] | Louisiana Turk Plant Prudence Review [Member]
Public Utilities, General Disclosures [Line Items]
LPSC Staff Recommended Potential Write-Off Range	$ 50.0
LPSC Staff Recommended Potential Refund Provisions Range	15.0
LPSC Staff Recommended Future Revenue Reductions Range	3.0
Subsequent Event [Member] | Minimum [Member] | Louisiana Turk Plant Prudence Review [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
LPSC Staff Recommended Potential Write-Off Range	50.0
LPSC Staff Recommended Potential Refund Provisions Range	15.0
LPSC Staff Recommended Future Revenue Reductions Range	3.0
Subsequent Event [Member] | Maximum [Member] | Louisiana Turk Plant Prudence Review [Member]
Public Utilities, General Disclosures [Line Items]
LPSC Staff Recommended Potential Write-Off Range	80.0
LPSC Staff Recommended Potential Refund Provisions Range	27.0
LPSC Staff Recommended Future Revenue Reductions Range	4.0
Subsequent Event [Member] | Maximum [Member] | Louisiana Turk Plant Prudence Review [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
LPSC Staff Recommended Potential Write-Off Range	80.0
LPSC Staff Recommended Potential Refund Provisions Range	27.0
LPSC Staff Recommended Future Revenue Reductions Range	$ 4.0